1. Field of the Invention
This invention pertains to the protection of iron materials exposed to harsh environments. More specifically, this invention pertains to materials and techniques used to protect ductile iron pipe buried underground which can be damaged by the environmental conditions created by various types of corrosive soil.
2. Prior Art
Iron pipes are used in many industries for the transportation of materials. Because of the obviously wide variety of applications, iron pipes are placed in many different environments, many of which are deleterious to the condition of the pipe. Particularly harsh environments can damage the pipe sufficiently to shorten its effective lifetime and require replacement earlier than might be expected. Replacement can be costly and inconvenient both in terms of excavating the pipe and the time lost while the pipe is out of operation. Therefore, protecting the pipe from damage caused by corrosion becomes a cost effective method of reducing the risks of using and relying on pipe.
Various methods and materials have been developed to create protective coverings for pipes. A typical method for protecting pipe involves providing an aluminum coating which is applied to an iron pipe, as exemplified by U.S. Pat. Nos. 4,755,224, 4,878,963 and 3,881,880. Aluminum is typically used as a pipe coating because it is noted for its ability to resist corrosion. In these patents, a thin layer is applied to an iron pipe before installation in a harsh environment, such as in or near salt water. Many of the protective aluminum coatings and their methods of application were even developed to enable the pipe to be used in high temperature environments.
The prior art also discloses protective pipe coatings that employ alloys so as to obtain the benefits offered by a combination of materials in a protective coating. For example, U.S. Pat. Nos. 4,891,274 and 5,234,514 utilize varying amounts of silicon and several other materials to create aluminum alloys that provide varying degrees of protection, as well as other benefits that aluminum alone can not provide.
Despite the development of corrosion resistant coatings, such as those described in the above-mentioned patents, the wide variety of corrosive soils having different corrosive properties which a single underground pipe might encounter can result in a protective pipe coating being perfectly suited for protecting a pipe at one location, and yet be inadequate for a different location, thus allowing damage to occur to the pipe.
Therefore, it would be an advantage over the prior art to not only develop a single protective coating that can withstand harsh soil conditions, but also provide protection in a wide variety of different corrosive soils.
In addition, when iron pipe is handled, installed or even after being placed underground, events often transpire which cause the relatively malleable aluminum protective coating to be pierced and exposed to the environment. Therefore, it would also be an advantage over the prior art if the protection of the exposed portions of the pipe could continue even in those potions of the pipe where the coating was accidentally removed.
It is an object of the present invention to provide a corrosion resistant protective coating for ductile iron materials that can be thermally sprayed on the pipe, where the coating provides long term protection from corrosive conditions.
It is also an object of the present invention to provide a corrosion resistant protective coating for ductile iron materials that can be arc sprayed on the pipe to achieve long term protection from corrosion.
It is another object of the present invention to provide a corrosion resistant protective coating for ductile iron materials formed as a pipe and installed in harsh and corrosive underground environmental conditions.
It is yet another object of the present invention to provide a protective coating for iron materials which provides protection in a variety of different corrosive and deleterious environments.
It is still another object of the present invention to provide a protective coating for ductile iron materials comprised of an aluminum-silicon alloy that does not suffer from intercrystalline corrosion.
Yet a further object of the present invention is to provide a protective pipe covering for iron materials comprised of an aluminum-silicon alloy which does not inhibit the film-forming capacity of the aluminum in corrosive environments.
Still another object of the present invention is to provide a protective coating for iron materials which can deposit an aluminum film to cover portions of pipe where the protective coating has been damaged or removed.
These and other objects and advantages of the present invention are realized in a corrosion resistant protective coating comprised of an aluminum-silicon alloy which is thermally sprayed or arc sprayed (using an air jet) on ductile iron materials such as piping which will be exposed to various corrosive environments. The pipe does not require any special preparations, other than being in a clean and oil free condition before the coating is applied. After application of the protective coating, a bituminous material such as asphalt is applied to further protect the pipe. The protective covering provides a barrier against corrosive soils that would otherwise damage the pipe, causing the pipe to fail or require replacement earlier than expected from normal use or exposure.
These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description.